Hyperphosphatemia frequently accompanies diseases associated with inadequate renal function, hyperparathyroidism, and certain other medical conditions. Hyperphosphatemia is typically defined for humans as a serum phosphate level of greater than about 4.5 mg/dL. The condition, especially if present over extended periods of time, leads to severe abnormalities in calcium and phosphorus metabolism and can be manifested by aberrant calcification in joints, lungs and eyes.
Anion exchange polymers, such as aliphatic amine polymers, have been used in the treatment of hyperphosphatemia. These polymers provide an effective treatment for decreasing the serum level of phosphate, without concomitantly increasing the absorption of any clinically undesirable materials.
Metabolic acidosis is another condition which accompanies diseases associated with inadequate renal function. The human body is constantly gaining H+ ions from the metabolism of sugars, fats, protein and lactic acid (produced under anaerobic metabolism). To maintain a constant pH the body must excrete H+ ions. Decreased excretion of H+ ions occurs in patients suffering from renal disease or renal failure, which results in metabolic acidosis and, hence, a low blood pH due to excess H+ ions.
Current treatments for hyperphosphatemia do not address the issue of metabolic acidosis. The present inventors have prepared carbonate salts of aliphatic amine polymers for this purpose, however, tablets made from carbonate salts of aliphatic amine polymers suffer from short shelf life. Further, the disintegration time of tablets made from carbonate salts increases over time when stored under standard storage conditions. This increase in disintegration time may lead to decreased availability of the active components of the drug to a patient.